The present invention relates to a developing head for electrophotographic apparatus which is capable of effectively supplying a liquid developing agent by a liquid feeding means.
Unlike conventional photographic film which uses silver halide photographic as the photosensitive member, electrophotographic material has a feature that it becomes photosensitive only after it is electrically charged. For these characteristics, a roll of elongated film is used as the electrophotographic material for microfilm which is charged, exposed, developed and fixed in part for recording an image, and serviced for projection of the thus obtained images together with unrecorded portions and images which are newly added to the unrecorded portions thereof.
So-called wet type electrophotographic apparatus which employs microfilm such as mentioned above develops electrostatic latent images by using a liquid developer and by charging, exposing, developing, drying and fixing the electrophotographic material frame by frame. It is therefore desirable that the liquid developer should not overflow from or leak into regions on the electrophotographic material other than where it should be treated for developing. It is also preferable that the excess liquid developer be removed as quickly as possible before the electrophotographic material is detached from the developing head and forwarded to subsequent processing sections.
FIG. 1(a) is a schematic view to show the structure of the developing head according to the prior art. As is shown in the figure, a developing head 1 is provided with a developing mask means 2. The developing mask means 2 has an opening with a frame 2a which is identical in size to one frame of an electrophotographic material 3 for an electrophotographic apparatus. The mouth 2b of the framed opening is in contact with the electrophotographic material 3. The outer frame surface 2c of the developing mask means 2 opposes the electrophotographic material 3 over a limited space. The inlet port 2d for liquid developer in the developing mask means 2 connects with the tip of a passageway 4. The base of the passageway is immersed in the liquid developer 5 pooled in a toner tank 7. The tip of a passageway 8 interposed with a pump 6 is connected to the outlet port 2e in the developing mask means 2, and the base thereof is located in the upper space of the toner tank 7. The inlet port 2d and the outlet port 2e for the liquid developer communicate via a passageway 2f. As the vacuum pump 6 is actuated, the pressure inside the chamber passageway 2f becomes negative, so that the liquid developer 5 is introduced into the chamber passageway 2f via the passageway 4 to come in contact with the electrophotographic material 3 which is formed with electrostatic latent images for developing in the developing chamber 2g which is an opening defined by the frame 2a. The liquid developer 5 after developing is sucked and returned to the toner tank 7 by the vacuum pump 6.
FIG. 2 is a schematic view to show the structure of another prior art developing head which is so structured as to remove the liquid developer 5 from the photosensitive surface 3a (hereinafter termed as squeezing).
As is shown in this figure, the developing head 1 of this type is provided with a developing mask means 2, which has an opening with a frame 2a identical in size with one frame of the electrophotographic material 3. The mouth 2b of the framed opening is in contact with the electrophotographic material 3. Thus, the photosensitive surface 3a which is one frame of the electrophotographic material 3 faces the developing chamber 2g. The liquid developer 5 is applied to the photosensitive surface 3a via the developing chamber 2g to obtain a predetermined latent image. In this case, the liquid developer 5 on the photosensitive surface 3a is then squeezed off from the surface 3a by injecting, for example, gas such as air onto the surface 3a. In order to do this, it is necessary to send the liquid developer 5 and the gas (in this case, air) into the developing chamber 2g. This is done by pumping up the liquid developer 5 pooled in the toner tank by means of the vacuum pump 6, which also draws the air in from the atmosphere as the valve 9 opens. In other words, there are provided passageways 4 and 8 which extend from the toner tank 7 into the developing mask means 2 and return to the toner tank 7 via the developing chamber 2g and the vacuum pump 6, and another passageway 10 which has its end portion opening into the atmosphere and extends into the developing mask means 2 via the valve 9 to joint the passageway 4 at the upstream from the developing chamber 2g. A pressing plate 12 abuts against the electrophotographic material 3 at its back to press the same toward the mouth 2b of the framed opening during developing and subsequent squeezing of the liquid developer 5. Its pressing is released when the electrophotographic material is advanced from one frame to the other for the next processing step.
On the other hand, the developing head 1 as shown in FIGS. 1(a) and 2 utilizes the vacuum pump 6 for feeding the liquid developer 5 or the liquid developer 5 and the gas for squeezing said agent. Because the vacuum pump 6 is expensive, the developing head 1 becomes costly and difficult to reduce in size as well as in price.
Such problems can be overcome if a compression-feeding means such as a liquid feeding pump is used instead of the vacuum pump 6, but this again entails other problems such as:
(a) As the liquid developer 5 is introduced into the developing chamber 2g under pressure applied by the compression means, there is danger that the liquid developer 5 might leak through the interstice between the mouth 2b of the framed opening and the photosensitive surface 3a. Such leakage would cause the liquid developer 5 to disperse over the entire area of said interstice by the capillarity since the interstice between the outer peripheral surface 2c and the electrophotographic material 3 is very narrow and the angle between the two is very small (ca. 5.degree.). The liquid developer 5 would eventually spread over the other areas of the electrophotographic that are not yet to be contacted with the liquid developer. Or, it may even flow into other parts of the electrophotographic apparatus. This is particularly marked in the developing head 1 shown in FIG. 1(a), the portion A thereof shown as an enlarged view in FIG. 1(b).
A developing head which is free from leakage of the liquid developer has been proposed, such as disclosed in Japanese Patent Publication No. Sho-51-13415, in which the mouth of the framed opening to be contacted with the electrophotographic material is made of a resilient member such as rubber. However, the use of a rubber mask at the mouth of the framed opening will involve an extra manufacturing process of pasting the rubber with adhesive. This will lead to a cost increase as well as trouble due to a stagnant liquid developer in the bonded portion and an inferior durability of the rubber mask. Also, if the developing head is made integral with the charging/exposing head, the use of a resilient member in the developing mask means results in unstable positioning of the electrophotographic material with respect to the developing head. This then affects the positioning of the lens with respect to the electrophotographic material which requires precision in reproduction.
(b) With the developing head 1 in which the liquid developer 5 is squeezed after developing such as shown in FIG. 2, the distance between the photosensitive surface 3a in the developing region and the developing electrode 11 is generally very narrow, whereby the liquid developer is likely to enter into the passageway 10 for feeding the gas because of the liquid resistance caused by the viscosity of the liquid developer. If the liquid developer enters into the pump, it would cause various problems, and the liquid developer entering into the passageway 10 would be jetted into the developing chamber 2g to reduce the squeezing efficiency when the pump is activated.
(c) Moreover, although the liquid developer 5 is squeezed by applying the gas to the photosensitive surface 3a, this is not sufficient. Squeezing may become adequate if sufficient time is allowed, but this too would cause another problem of reduced processing efficiency per unit time.
U.S. Pat. No. 3,916,828 and U.S. Pat. No. 4,141,647 are referred to as the prior art in relation to FIG. 1 or 2.